1. Field of the Invention
The present invention relates to the field of gas-turbine technology. It relates to a burner arrangement for a gas turbine, where the burner arrangement comprises a interior space enclosed by a casing, in which interior space at least one burner is arranged, and into which interior space in each case a jet of a gaseous medium, in particular air, is sprayed through at least two nozzle openings against the direction of flow of the burner and along the inner wall of the casing, which jets, guided by the inner wall, meet one another from opposite directions and combine to form a secondary flow flowing off perpendicularly from the inner wall.
Such a burner arrangement has been disclosed, for example, by publication EP-A2-0 692 675 (see, for example, FIG. 1 there).
2. Discussion of Background
A double-cone burner of a gas turbine, to which double-cone burner fuel is fed via a fuel lance, is shown in the publication mentioned at the beginning (e.g. in FIG. 1 there). The burner is accommodated in the interior space of a dome-like casing. Main burner air flows into the casing against the direction of flow of the burner above and below the burner, is deflected by the inner wall of the casing and then enters the burner in order to be mixed with the fuel there.
Such a flow in a casing, which flow results from two or more jets striking one another, the jets entering the casing through corresponding nozzle openings, is generally extremely sensitive to fluctuations in the total pressure of the jets. This may be illustrated with reference to FIG. 1. In the flow arrangement 10 according to FIG. 1, two jets 15, 16 are sprayed on two opposite sides through corresponding nozzle openings 13, 14 into an interior space 11, which is defined by a boundary wall 12 (curved in a semicircle in this example), and these jets 15, 16--guided by the boundary wall 12--meet one another at an impingement point 18 and combine there to form a secondary flow 17, which is directed perpendicularly to the boundary wall into the interior of the interior space 11.
The velocity of the jets 15, 16 approaches zero at the impingement point 18. Since the wall streamlines of the two jets 15 and 16 meet at the stagnation point 18, the total pressures of the jets 15 and 16 must also correspond there. Since the friction at the boundary wall 12 typically does not lead to a rapid change in the total pressure, the impingement point 18 will regularly lie in the vicinity of one of the two nozzle openings 13, 14, which produce the jets 15, 16. In the extreme case, one of the jets 15, 16 may even block the nozzle opening which is intended to produce the other jet. Even in the cases in which the total pressures of the two jets are virtually the same, the position of the impingement point normally deviates greatly from the plane of symmetry which runs between the two nozzle openings.
This instability and uncertainty of such casing flows also has an effect in the case of a burner arrangement 20 as shown in FIG. 2. The burner 21 (in this case a double-cone burner of known type of construction) is accommodated in a casing 23 in such a way as to lie in a plane of symmetry 19. The burner 21 opens to the left into a combustion chamber 33; it is supplied with fuel from the right via a fuel feed 32. Formed at the top and bottom between the combustion chamber 33 and the casing 23 are nozzle openings 24 and 25, through which combustion air (from the compressor of the gas turbine) is sprayed in the form of jets 26, 27 into the interior space 22 enclosed by the casing 23. The jets 26, 27 flow toward one another along the inner wall 23a of the casing 23 and, after striking one another, combine to form a secondary flow 28, which flows toward the burner 21 and enters the burner 21 laterally. As indicated in FIG. 2, the impingement point and thus also the secondary flow generally lie at a varying point outside the plane of symmetry, which point cannot be predetermined and may change quickly due to geometric disturbances in the arrangement and due to pressure fluctuations. As a result, the uniform operation of the burner 21 under stable combustion conditions is considerably impaired.